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Published September 21, 2014 | Submitted + Published
Journal Article Open

The VLA-COSMOS Survey - V. 324 MHz continuum observations


We present 90 cm Very Large Array imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0 arcsec × 6.0 arcsec angular resolution with an average rms of 0.5 mJy beam⁻¹. The extracted catalogue contains 182 sources (down to 5.5σ), 30 of which are multicomponent sources. Using Monte Carlo artificial source simulations, we derive the completeness of the catalogue, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV–NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei. The average 90–20 cm spectral index (S_ν ∝ ν^α, where S_ν is the flux density at frequency ν and α the spectral index) of our 90 cm selected sources is −0.70, with an interquartile range from −0.90 to −0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than −1 all lie at z ≳ 1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z ≳ 1).

Additional Information

© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 July 1. Received 2014 June 23; in original form 2014 April 1. First published online August 4, 2014. VS acknowledges the European Unions Seventh Frame-work programme grant agreement 333654 (CIG, 'AGN feedback') and the Australian Group of Eight European Fellowship 2013. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. AK acknowledges support by the Collaborative Research Council 956, sub-project A1, funded by the Deutsche Forschungsgemeinschaft (DFG).

Attached Files

Published - MNRAS-2014-Smol_i_-2590-8.pdf

Submitted - 1407.4844v1.pdf


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